The present invention relates generally to phase and frequency synchronization techniques for PSK (phase-shift keying) demodulators, and more specifically to a coherent PSK demodulator suitable for satellite communications systems.
Phase-locked loops have been extensively used for establishing synchronization with the phase and frequency of an incoming PSK modulated signal. The synchronization characteristic of a phase-locked loop at low signal-to-noise ratios is considered as a factor that contradicts the pull-in characteristic of the loop for a wide range of frequencies. Another disadvantage is that the phase-locked loop has a significantly long pull-in time when the signal-to-noise ratio is low. In addition, a large carrier frequency offset, which occurs often in satellite communications systems, results in a narrowing of the capture range of the phase-locked loop, and hence in a further lengthening of the pull-in time.